diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index efe0d5f7d..ef2ba3855 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -9,7 +9,7 @@ repos:
   - id: check-yaml
   - id: check-added-large-files
 - repo: https://github.com/pre-commit/mirrors-clang-format
-  rev: v20.1.8
+  rev: v21.1.0
   hooks:
   - id: clang-format
     types_or: [c++, c]
diff --git a/src/Context.h b/src/Context.h
index a456364e9..61933400c 100644
--- a/src/Context.h
+++ b/src/Context.h
@@ -46,36 +46,36 @@ class Context {
   Context() = default;  // Default constructor
   ~Context();           // Destructor
 
-  Context(const Context &);
-  Context &operator=(const Context &);
+  Context(const Context&);
+  Context& operator=(const Context&);
 
-  static Context &getContext();
-  static void setContext(Context *);
+  static Context& getContext();
+  static void setContext(Context*);
 
-  int initialize(int, const char **);  // all startup
+  int initialize(int, const char**);  // all startup
   int run();
-  int dispatch(std::string &);  // command handler dispatch
+  int dispatch(std::string&);  // command handler dispatch
 
   int getWidth();   // determine terminal width
   int getHeight();  // determine terminal height
 
-  std::string getTaskContext(const std::string &, std::string, bool fallback = true);
+  std::string getTaskContext(const std::string&, std::string, bool fallback = true);
 
   const std::vector<std::string> getColumns() const;
-  void getLimits(int &, int &);
+  void getLimits(int&, int&);
 
-  bool color();                       // TTY or <other>?
-  bool verbose(const std::string &);  // Verbosity control
+  bool color();                      // TTY or <other>?
+  bool verbose(const std::string&);  // Verbosity control
 
-  void header(const std::string &);    // Header message sink
-  void footnote(const std::string &);  // Footnote message sink
-  void debug(const std::string &);     // Debug message sink
-  void error(const std::string &);     // Error message sink - non-maskable
+  void header(const std::string&);    // Header message sink
+  void footnote(const std::string&);  // Footnote message sink
+  void debug(const std::string&);     // Debug message sink
+  void error(const std::string&);     // Error message sink - non-maskable
 
-  void decomposeSortField(const std::string &, std::string &, bool &, bool &);
-  void debugTiming(const std::string &, const Timer &);
+  void decomposeSortField(const std::string&, std::string&, bool&, bool&);
+  void debugTiming(const std::string&, const Timer&);
 
-  CurrentTask withCurrentTask(const Task *);
+  CurrentTask withCurrentTask(const Task*);
   friend class CurrentTask;
 
  private:
@@ -86,7 +86,7 @@ class Context {
   void loadAliases();
   void propagateDebug();
 
-  static Context *context;
+  static Context* context;
 
  public:
   CLI2 cli2{};
@@ -104,8 +104,8 @@ class Context {
   std::vector<std::string> footnotes{};
   std::vector<std::string> errors{};
   std::vector<std::string> debugMessages{};
-  std::map<std::string, Command *> commands{};
-  std::map<std::string, Column *> columns{};
+  std::map<std::string, Command*> commands{};
+  std::map<std::string, Column*> columns{};
   int terminal_width{0};
   int terminal_height{0};
 
@@ -121,7 +121,7 @@ class Context {
   long time_hooks_us{0};
 
   // the current task for DOM references, or NULL if there is no task
-  const Task *currentTask{NULL};
+  const Task* currentTask{NULL};
 };
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -132,10 +132,10 @@ class CurrentTask {
   ~CurrentTask();
 
  private:
-  CurrentTask(Context &context, const Task *previous);
+  CurrentTask(Context& context, const Task* previous);
 
-  Context &context;
-  const Task *previous;
+  Context& context;
+  const Task* previous;
 
   friend class Context;
 };
diff --git a/src/Eval.h b/src/Eval.h
index 3203e8a15..85fe96721 100644
--- a/src/Eval.h
+++ b/src/Eval.h
@@ -33,43 +33,43 @@
 #include <string>
 #include <vector>
 
-bool domSource(const std::string &, Variant &);
+bool domSource(const std::string&, Variant&);
 
 class Eval {
  public:
   Eval();
 
-  void addSource(bool (*fn)(const std::string &, Variant &));
-  void evaluateInfixExpression(const std::string &, Variant &) const;
-  void evaluatePostfixExpression(const std::string &, Variant &) const;
-  void compileExpression(const std::vector<std::pair<std::string, Lexer::Type>> &);
-  void evaluateCompiledExpression(Variant &);
+  void addSource(bool (*fn)(const std::string&, Variant&));
+  void evaluateInfixExpression(const std::string&, Variant&) const;
+  void evaluatePostfixExpression(const std::string&, Variant&) const;
+  void compileExpression(const std::vector<std::pair<std::string, Lexer::Type>>&);
+  void evaluateCompiledExpression(Variant&);
   void debug(bool);
 
   static std::vector<std::string> getOperators();
   static std::vector<std::string> getBinaryOperators();
 
  private:
-  void evaluatePostfixStack(const std::vector<std::pair<std::string, Lexer::Type>> &,
-                            Variant &) const;
-  void infixToPostfix(std::vector<std::pair<std::string, Lexer::Type>> &) const;
-  void infixParse(std::vector<std::pair<std::string, Lexer::Type>> &) const;
-  bool parseLogical(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseRegex(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseEquality(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseComparative(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseArithmetic(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseGeometric(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseTag(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseUnary(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parseExponent(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool parsePrimitive(std::vector<std::pair<std::string, Lexer::Type>> &, unsigned int &) const;
-  bool identifyOperator(const std::string &, char &, unsigned int &, char &) const;
+  void evaluatePostfixStack(const std::vector<std::pair<std::string, Lexer::Type>>&,
+                            Variant&) const;
+  void infixToPostfix(std::vector<std::pair<std::string, Lexer::Type>>&) const;
+  void infixParse(std::vector<std::pair<std::string, Lexer::Type>>&) const;
+  bool parseLogical(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseRegex(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseEquality(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseComparative(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseArithmetic(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseGeometric(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseTag(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseUnary(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parseExponent(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool parsePrimitive(std::vector<std::pair<std::string, Lexer::Type>>&, unsigned int&) const;
+  bool identifyOperator(const std::string&, char&, unsigned int&, char&) const;
 
-  std::string dump(std::vector<std::pair<std::string, Lexer::Type>> &) const;
+  std::string dump(std::vector<std::pair<std::string, Lexer::Type>>&) const;
 
  private:
-  std::vector<bool (*)(const std::string &, Variant &)> _sources{};
+  std::vector<bool (*)(const std::string&, Variant&)> _sources{};
   bool _debug{false};
   std::vector<std::pair<std::string, Lexer::Type>> _compiled{};
 };
diff --git a/src/Operation.h b/src/Operation.h
index 82c2ea022..b6588e93f 100644
--- a/src/Operation.h
+++ b/src/Operation.h
@@ -39,14 +39,14 @@
 // type.
 class Operation {
  public:
-  explicit Operation(const tc::Operation &);
+  explicit Operation(const tc::Operation&);
 
-  Operation(const Operation &other) = default;
-  Operation &operator=(const Operation &other);
+  Operation(const Operation& other) = default;
+  Operation& operator=(const Operation& other);
 
   // Create a vector of Operations given the result of `Replica::get_undo_operations` or
   // `Replica::get_task_operations`. The resulting vector must not outlive the input `rust::Vec`.
-  static std::vector<Operation> operations(const rust::Vec<tc::Operation> &);
+  static std::vector<Operation> operations(const rust::Vec<tc::Operation>&);
 
   // Methods from the underlying `tc::Operation`.
   bool is_create() const { return op->is_create(); }
@@ -79,10 +79,10 @@ class Operation {
   // Define a partial order on Operations:
   //  - Create < Update < Delete < UndoPoint
   //  - Given two updates, sort by timestamp
-  bool operator<(const Operation &other) const;
+  bool operator<(const Operation& other) const;
 
  private:
-  const tc::Operation *op;
+  const tc::Operation* op;
 };
 
 #endif
diff --git a/src/TDB2.h b/src/TDB2.h
index 51669ab6d..fc9e8e132 100644
--- a/src/TDB2.h
+++ b/src/TDB2.h
@@ -44,12 +44,12 @@ class TDB2 {
 
   TDB2() = default;
 
-  void open_replica(const std::string &, bool create_if_missing, bool read_write);
+  void open_replica(const std::string&, bool create_if_missing, bool read_write);
   void open_replica_in_memory();
-  void add(Task &);
-  void modify(Task &);
-  void purge(Task &);
-  void get_changes(std::vector<Task> &);
+  void add(Task&);
+  void modify(Task&);
+  void purge(Task&);
+  void get_changes(std::vector<Task>&);
   void gc();
   void expire_tasks();
   int latest_id();
@@ -58,20 +58,20 @@ class TDB2 {
   const std::vector<Task> all_tasks();
   const std::vector<Task> pending_tasks();
   const std::vector<Task> completed_tasks();
-  bool get(int, Task &);
-  bool get(const std::string &, Task &);
-  bool has(const std::string &);
-  const std::vector<Task> siblings(Task &);
-  const std::vector<Task> children(Task &);
+  bool get(int, Task&);
+  bool get(const std::string&, Task&);
+  bool has(const std::string&);
+  const std::vector<Task> siblings(Task&);
+  const std::vector<Task> children(Task&);
 
   // ID <--> UUID mapping.
   std::string uuid(int);
-  int id(const std::string &);
+  int id(const std::string&);
 
   int num_local_changes();
   int num_reverts_possible();
 
-  rust::Box<tc::Replica> &replica();
+  rust::Box<tc::Replica>& replica();
 
  private:
   std::optional<rust::Box<tc::Replica>> _replica;
@@ -85,8 +85,8 @@ class TDB2 {
   // UUID -> Task containing all tasks modified in this invocation.
   std::map<std::string, Task> changes;
 
-  const rust::Box<tc::WorkingSet> &working_set();
-  void maybe_add_undo_point(rust::Vec<tc::Operation> &);
+  const rust::Box<tc::WorkingSet>& working_set();
+  void maybe_add_undo_point(rust::Vec<tc::Operation>&);
 };
 
 #endif
diff --git a/src/Version.cpp b/src/Version.cpp
index e1633f86c..f3cff0ba4 100644
--- a/src/Version.cpp
+++ b/src/Version.cpp
@@ -66,32 +66,32 @@ Version Version::Current() { return Version(PACKAGE_VERSION); }
 bool Version::is_valid() const { return major >= 0; }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator<(const Version &other) const {
+bool Version::operator<(const Version& other) const {
   return std::tie(major, minor, patch) < std::tie(other.major, other.minor, other.patch);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator<=(const Version &other) const {
+bool Version::operator<=(const Version& other) const {
   return std::tie(major, minor, patch) <= std::tie(other.major, other.minor, other.patch);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator>(const Version &other) const {
+bool Version::operator>(const Version& other) const {
   return std::tie(major, minor, patch) > std::tie(other.major, other.minor, other.patch);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator>=(const Version &other) const {
+bool Version::operator>=(const Version& other) const {
   return std::tie(major, minor, patch) >= std::tie(other.major, other.minor, other.patch);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator==(const Version &other) const {
+bool Version::operator==(const Version& other) const {
   return std::tie(major, minor, patch) == std::tie(other.major, other.minor, other.patch);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-bool Version::operator!=(const Version &other) const {
+bool Version::operator!=(const Version& other) const {
   return std::tie(major, minor, patch) != std::tie(other.major, other.minor, other.patch);
 }
 
@@ -107,7 +107,7 @@ Version::operator std::string() const {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-std::ostream &operator<<(std::ostream &os, const Version &version) {
+std::ostream& operator<<(std::ostream& os, const Version& version) {
   os << std::string(version);
   return os;
 }
diff --git a/src/Version.h b/src/Version.h
index 03b81d2ad..e5f040295 100644
--- a/src/Version.h
+++ b/src/Version.h
@@ -39,10 +39,10 @@ class Version {
   // Create an invalid version.
   Version() = default;
 
-  Version(const Version &other) = default;
-  Version(Version &&other) = default;
-  Version &operator=(const Version &) = default;
-  Version &operator=(Version &&) = default;
+  Version(const Version& other) = default;
+  Version(Version&& other) = default;
+  Version& operator=(const Version&) = default;
+  Version& operator=(Version&&) = default;
 
   // Return a version representing the release being built.
   static Version Current();
@@ -50,17 +50,17 @@ class Version {
   bool is_valid() const;
 
   // Compare versions.
-  bool operator<(const Version &) const;
-  bool operator<=(const Version &) const;
-  bool operator>(const Version &) const;
-  bool operator>=(const Version &) const;
-  bool operator==(const Version &) const;
-  bool operator!=(const Version &) const;
+  bool operator<(const Version&) const;
+  bool operator<=(const Version&) const;
+  bool operator>(const Version&) const;
+  bool operator>=(const Version&) const;
+  bool operator==(const Version&) const;
+  bool operator!=(const Version&) const;
 
   // Convert back to a string.
   operator std::string() const;
 
-  friend std::ostream &operator<<(std::ostream &os, const Version &version);
+  friend std::ostream& operator<<(std::ostream& os, const Version& version);
 
  private:
   int major = -1;
diff --git a/src/commands/CmdImportV2.h b/src/commands/CmdImportV2.h
index 5cfddd63d..5691b52b5 100644
--- a/src/commands/CmdImportV2.h
+++ b/src/commands/CmdImportV2.h
@@ -35,10 +35,10 @@
 class CmdImportV2 : public Command {
  public:
   CmdImportV2();
-  int execute(std::string &);
+  int execute(std::string&);
 
  private:
-  int import(const std::vector<std::map<std::string, std::string>> &task_data);
+  int import(const std::vector<std::map<std::string, std::string>>& task_data);
 };
 
 #endif
diff --git a/src/commands/CmdModify.cpp b/src/commands/CmdModify.cpp
index a962ea10b..f2bd3f025 100644
--- a/src/commands/CmdModify.cpp
+++ b/src/commands/CmdModify.cpp
@@ -58,7 +58,7 @@ CmdModify::CmdModify() {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-int CmdModify::execute(std::string &) {
+int CmdModify::execute(std::string&) {
   auto rc = 0;
 
   // Apply filter.
@@ -77,7 +77,7 @@ int CmdModify::execute(std::string &) {
   if (filtered.size() > 1) {
     feedback_affected("This command will alter {1} tasks.", filtered.size());
   }
-  for (auto &task : filtered) {
+  for (auto& task : filtered) {
     Task before(task);
     task.modify(Task::modReplace);
 
@@ -99,7 +99,7 @@ int CmdModify::execute(std::string &) {
   }
 
   // Now list the project changes.
-  for (const auto &change : projectChanges)
+  for (const auto& change : projectChanges)
     if (change.first != "") Context::getContext().footnote(change.second);
 
   feedback_affected(count == 1 ? "Modified {1} task." : "Modified {1} tasks.", count);
@@ -108,7 +108,7 @@ int CmdModify::execute(std::string &) {
 
 ////////////////////////////////////////////////////////////////////////////////
 // TODO Why is this not in Task::validate?
-void CmdModify::checkConsistency(Task &before, Task &after) {
+void CmdModify::checkConsistency(Task& before, Task& after) {
   // Perform some logical consistency checks.
   if (after.has("recur") && !after.has("due") && !before.has("due"))
     throw std::string("You cannot specify a recurring task without a due date.");
@@ -126,8 +126,8 @@ void CmdModify::checkConsistency(Task &before, Task &after) {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-int CmdModify::modifyAndUpdate(Task &before, Task &after,
-                               std::map<std::string, std::string> *projectChanges /* = NULL */) {
+int CmdModify::modifyAndUpdate(Task& before, Task& after,
+                               std::map<std::string, std::string>* projectChanges /* = NULL */) {
   // This task.
   auto count = 1;
 
@@ -150,14 +150,14 @@ int CmdModify::modifyAndUpdate(Task &before, Task &after,
 
 ////////////////////////////////////////////////////////////////////////////////
 int CmdModify::modifyRecurrenceSiblings(
-    Task &task, std::map<std::string, std::string> *projectChanges /* = NULL */) {
+    Task& task, std::map<std::string, std::string>* projectChanges /* = NULL */) {
   auto count = 0;
 
   if ((Context::getContext().config.get("recurrence.confirmation") == "prompt" &&
        confirm(STRING_CMD_MODIFY_RECUR)) ||
       Context::getContext().config.getBoolean("recurrence.confirmation")) {
     std::vector<Task> siblings = Context::getContext().tdb2.siblings(task);
-    for (auto &sibling : siblings) {
+    for (auto& sibling : siblings) {
       Task alternate(sibling);
       sibling.modify(Task::modReplace);
       updateRecurrenceMask(sibling);
@@ -181,7 +181,7 @@ int CmdModify::modifyRecurrenceSiblings(
 
 ////////////////////////////////////////////////////////////////////////////////
 int CmdModify::modifyRecurrenceParent(
-    Task &task, std::map<std::string, std::string> *projectChanges /* = NULL */) {
+    Task& task, std::map<std::string, std::string>* projectChanges /* = NULL */) {
   auto count = 0;
 
   auto children = Context::getContext().tdb2.children(task);
@@ -189,7 +189,7 @@ int CmdModify::modifyRecurrenceParent(
       ((Context::getContext().config.get("recurrence.confirmation") == "prompt" &&
         confirm(STRING_CMD_MODIFY_RECUR)) ||
        Context::getContext().config.getBoolean("recurrence.confirmation"))) {
-    for (auto &child : children) {
+    for (auto& child : children) {
       Task alternate(child);
       child.modify(Task::modReplace);
       updateRecurrenceMask(child);
diff --git a/src/commands/CmdModify.h b/src/commands/CmdModify.h
index 17313e798..0e33d877f 100644
--- a/src/commands/CmdModify.h
+++ b/src/commands/CmdModify.h
@@ -34,14 +34,14 @@
 class CmdModify : public Command {
  public:
   CmdModify();
-  int execute(std::string &);
-  void checkConsistency(Task &before, Task &after);
-  int modifyAndUpdate(Task &before, Task &after,
-                      std::map<std::string, std::string> *projectChanges = nullptr);
-  int modifyRecurrenceSiblings(Task &task,
-                               std::map<std::string, std::string> *projectChanges = nullptr);
-  int modifyRecurrenceParent(Task &task,
-                             std::map<std::string, std::string> *projectChanges = nullptr);
+  int execute(std::string&);
+  void checkConsistency(Task& before, Task& after);
+  int modifyAndUpdate(Task& before, Task& after,
+                      std::map<std::string, std::string>* projectChanges = nullptr);
+  int modifyRecurrenceSiblings(Task& task,
+                               std::map<std::string, std::string>* projectChanges = nullptr);
+  int modifyRecurrenceParent(Task& task,
+                             std::map<std::string, std::string>* projectChanges = nullptr);
 };
 
 #endif
diff --git a/src/commands/CmdUndo.h b/src/commands/CmdUndo.h
index 590184178..e82655393 100644
--- a/src/commands/CmdUndo.h
+++ b/src/commands/CmdUndo.h
@@ -36,10 +36,10 @@
 class CmdUndo : public Command {
  public:
   CmdUndo();
-  int execute(std::string &);
+  int execute(std::string&);
 
  private:
-  bool confirm_revert(const std::vector<Operation> &);
+  bool confirm_revert(const std::vector<Operation>&);
 };
 
 #endif
diff --git a/test/make_tc_task.cpp b/test/make_tc_task.cpp
index 37f1d963f..661a7595f 100644
--- a/test/make_tc_task.cpp
+++ b/test/make_tc_task.cpp
@@ -46,11 +46,11 @@ int usage() {
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
-int main(int argc, char **argv) {
+int main(int argc, char** argv) {
   if (!--argc) {
     return usage();
   }
-  char *datadir = *++argv;
+  char* datadir = *++argv;
 
   auto replica = tc::new_replica_on_disk(datadir, /*create_if_missing=*/true, /*read_write=*/true);
   auto uuid = tc::uuid_v4();
diff --git a/test/tc_cpp_test.cpp b/test/tc_cpp_test.cpp
index c92e5e66d..7059ed48d 100644
--- a/test/tc_cpp_test.cpp
+++ b/test/tc_cpp_test.cpp
@@ -41,7 +41,7 @@ std::string uuid2str(tc::Uuid uuid) { return static_cast<std::string>(uuid.to_st
 // Tests for the basic cxxbridge functionality. This focuses on the methods with
 // complex cxxbridge implementations, rather than those with complex Rust
 // implementations but simple APIs, like sync.
-int TEST_NAME(int, char **) {
+int TEST_NAME(int, char**) {
   UnitTest t;
   std::string str;
 
@@ -94,7 +94,7 @@ int TEST_NAME(int, char **) {
   auto old_task = ops[5].get_old_task();
   // old_task is in arbitrary order, so just check that status is in there.
   bool found = false;
-  for (auto &pv : old_task) {
+  for (auto& pv : old_task) {
     std::string p = static_cast<std::string>(pv.prop);
     if (p == "status") {
       std::string v = static_cast<std::string>(pv.value);
@@ -131,7 +131,7 @@ int TEST_NAME(int, char **) {
 
   auto all_tasks = replica->all_task_data();
   t.is(all_tasks.size(), (size_t)2, "now there are 2 tasks");
-  for (auto &maybe_task : all_tasks) {
+  for (auto& maybe_task : all_tasks) {
     t.ok(maybe_task.is_some(), "all_tasks is fully populated");
     auto task = maybe_task.take();
     if (task->get_uuid() == uuid) {
@@ -144,7 +144,7 @@ int TEST_NAME(int, char **) {
   try {
     replica->sync_to_local("/does/not/exist", false);
     // tc::new_replica_on_disk("/does/not/exist", false);
-  } catch (rust::Error &err) {
+  } catch (rust::Error& err) {
     t.is(err.what(),
          "unable to open database file: /does/not/exist/taskchampion-local-sync-server.sqlite3: "
          "Error code 14: Unable to open the database file",